Integrated circuit density continues to be limited by the “real estate” available for mounting individual integrated circuits on a substrate. Even larger form factor systems, such as PC's, compute servers, and storage servers, need more integrated circuits in the same or smaller “real estate”. Particularly acute, the needs for portable personal electronics, such as cell phones, digital cameras, music players, PDA's, and location-based devices, have further driven the need for integrated circuit density.
To this end, wafer level chip scale packages (WLCSPs) have been developed that are similar to the solder-bumped flip chip, except that the solder bumps on a WLCSP are much larger. The printed circuit board assembly of a WLCSP is more robust, and underfill encapsulants do not present a problem. WLCSP and flip chip manufacturing share common components and techniques, particularly solder bumping.
A flip chip microelectronic assembly includes a direct electrical connection of face down (that is, “flipped”) electronic components onto substrates, such as ceramic substrates, circuit boards, or carriers using conductive bump bond pads of the chip. The flip chip components used in flip chip microelectronic assemblies are predominantly semiconductor devices, however, components such as passive filters, detector arrays, and MEM devices are being used in flip chip form. Flip chips are also known as “direct chip attach” because the chip is directly attached to the substrate, board, or carrier by the conductive bumps.
The use of flip chip packaging has dramatically grown because of the flip chip's advantages in size, performance, flexibility, reliability, and cost over other packaging methods and from the widening availability of flip chip materials, equipment, and services. In some cases, the elimination of old technology packages and bond wires may reduce the substrate or board area needed to secure the device by up to 25 percent, and may require far less height. Further, the weight of the flip chip can be less than 5 percent of the old technology package devices.
The bumps of the flip chip assembly serve several functions. The bumps provide an electrical conductive path from the chip (or die) to the substrate on which the chip is mounted. A thermally conductive path is also provided by the bumps to carry heat from the chip to the substrate. The bumps also provide part of the mechanical mounting of the chip to the substrate. A spacer is provided by the bumps that prevents electrical contact between the chip and the substrate connectors. Finally, the bumps act as a short lead to relieve mechanical strain between the chip and the substrate.
Protective metallurgy layers may be provided over the bond pad. Ball limiting metallurgy (BLM) or under bump metallurgy (UBM) generally consists of successive layers. The “adhesion” layer must adhere well to both the bond pad metal and the surrounding passivation, provide a strong, low-stress mechanical and electrical connection. The “diffusion barrier” layer prevents the diffusion of solder into the underlying material. The “solder wettable” layer provides a wettable surface for the molten solder during the solder bumping process, for good bonding of the solder to the underlying metal.
A number of problems have arisen when reducing size but maintaining big bumps on redistribution layers for wafer level chip scale packages including early failures.
Thus, a need still remains for an integrated circuit package system to provide improved stability and small isolated feature deposition. In view of the ever-increasing commercial competitive pressures, along with growing consumer expectations and the diminishing opportunities for meaningful product differentiation in the marketplace, it is critical that answers be found for these problems. Additionally, the need to save costs, improve efficiencies and performance, and meet competitive pressures, adds an even greater urgency to the critical necessity for finding answers to these problems.
Solutions to these problems have been long sought but prior developments have not taught or suggested any solutions and, thus, solutions to these problems have long eluded those skilled in the art.